Method for depositing and curing nanoparticle-based ink using spatial light modulator

ABSTRACT

An apparatus for forming a pattern of a nanoparticle ink on a substrate has a transport apparatus that is energizable to move the substrate in a direction and a printing apparatus that deposits the nanoparticle ink in a pattern on a surface of the moving substrate. An illumination apparatus directs a patterned illumination to cure the deposited ink pattern on the moving substrate, the illumination apparatus having a light source that generates light directed toward a uniformizer, a spatial light modulator energizable to form a patterned illumination from the uniformized light, and an illumination lens disposed to direct illumination from the spatial light modulator onto the surface of the moving substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/661,378, filed on Jun. 19, 2012, entitled “AMETHOD FOR DEPOSITING AND SINTERING NANO PARTICLE BASED INK” in thenames of Sujatha Ramanuj an et al., the contents of which areincorporated fully herein by reference.

FIELD OF THE INVENTION

This invention relates in general to an apparatus and method fordepositing electronic ink onto media, and sintering the ink by means ofa spatially and temporally modulating a light beam.

BACKGROUND

Fabrication of mass-produced electronic items typically involvestemperature- and atmosphere-sensitive processing. Conventional materialdeposition systems for electronic fabrication, including plasma-enhancedchemical vapor deposition PECVD and other vacuum deposition processes,rely on high temperatures and rigidly controlled ambient conditions.Conventional processes are typically subtractive, applying a conductiveor other coating over a surface, treating the coating to form a pattern,then removing unwanted material. The conventional method for formingcopper traces is one example of this process, requiring multipleprocessing steps with the use of toxic chemicals and the complicationsand cost of proper waste disposal.

Recent advances in printed electronics provide solutions that reduce thecost, complexity, and energy requirements of conventional depositionmethods and expand the range of substrate materials that can be used.For printed electronics, materials can be deposited and cured attemperatures compatible with paper and plastic substrates and can behandled in air. In particular, advances with nanoparticle-based inks,such as silver, copper, and other metal nanoparticle-based inks, forexample, make it feasible to print electronic circuit structures usingstandard additive printing systems such as inkjet and screen printingsystems. Advantageously, nanoparticle-based inks have lower curingtemperatures than those typically needed for bulk curing where largerparticles of the same material are used.

Commercially available systems for curing nanoparticles typically employheat from convection ovens or Xenon flash illumination energy. In suchillumination systems, the Xenon lamps emit pulsed light that is directedonto films of nanoparticles to be cured. High light energy levels arerequired for nanoparticle curing. Exemplary nanoparticle-based inks suchas Intrinsiq Material Ltd. CI-002, a copper nanoparticle based inkjetink, or CP-001, a copper nanoparticle-based screen print ink, can besintered through the use of photonic energy from Xenon lamp or otherillumination, provided that the illumination system delivers adequateenergy to volatilize coatings used in the ink formulations and to sinterand cure the inks over large surface areas.

Conventional approaches for conditioning of the nanoparticle material,however, suffer from a number of deficiencies. Xenon lamp emission ischaracteristically distributed over a broad range of wavelengths andoften includes wavelengths that can cause unwanted effects, even atnon-peak energy levels. This inherent spectral spread in Xenon lampemission can have effects that result in incomplete or uneven curing.One result can be limited penetration of light energy into thicker filmsor premature sealing of top surface layers, trapping unwanted organicspecies in the remaining structure. This type of problem can occur whenhigher frequency light, such as light energy from the tail of thespectral distribution, inadvertently sinters the film and renders itstop layers opaque to other wavelengths of emitted Xenon light, delayingor preventing curing of the lower layers. When this happens, the binderor organic suspension in which nanoparticles are suspended is onlypartially removed, causing uneven sintering, which can limit theconductivity of the applied materials.

With Xenon light, the distribution of energy intensity isnon-symmetrical; the co-lateral dispersive energy that is produced canreduce curing efficiency or may even cause overheating and damage to thesubstrate. Further, pulsing of the Xenon lamp or other light sourcetends to create high energy peaks that can ablate films rather than meltand reflow films. As a result, the cured product may not have thedesired structure.

Conventional methods are also limited with respect to the number ofsubstrates that can be used. With materials having high thermalconductivity, such as aluminum, silicon, and ceramics, the appliedenergy intended for curing may dissipate too quickly. With suchmaterials, heat can be drawn away from the area of incident light beforesintering occurs. Furthermore, particular wavelengths emitted from theXenon lamps can damage some polymeric films and other substrates, makingthem less suitable for curing.

Thus, it can be seen that there is a need for improved methods forsintering and curing nanoparticulate inks and similar materials.

SUMMARY OF THE INVENTION

It is an object of the present invention to advance the art of sinteringand curing nanoparticle-based inks. With this object in mind,embodiments of the present invention provide an apparatus for forming apattern of a nanoparticle ink on a substrate, the apparatus comprising:

-   -   a transport apparatus that is energizable to move the substrate        in a direction;    -   a printing apparatus that deposits the nanoparticle ink in a        pattern on a surface of the moving substrate; and    -   an illumination apparatus that directs a patterned illumination        to cure the deposited ink pattern on the moving substrate, the        illumination apparatus having:        -   (i) a light source that generates light directed toward a            uniformizer;        -   (ii) a spatial light modulator energizable to form a            patterned illumination from the uniformized light;        -   (iii) an illumination lens disposed to direct illumination            from the spatial light modulator onto the surface of the            moving substrate.

From an alternate aspect, the present invention provides a method forforming a pattern of a nanoparticle ink on a substrate, the methodcomprising:

-   -   energizing a transport apparatus to move the substrate in a        direction;    -   depositing the nanoparticle ink in a pattern on a surface of the        moving substrate; and    -   curing the deposited ink pattern on the moving substrate by:        -   (i) generating light and directing the light toward a            uniformizer;        -   (ii) energizing a spatial light modulator to form a            patterned illumination from the uniformized light; and        -   (iii) directing the patterned illumination from the spatial            light modulator onto the surface of the moving substrate.

Among advantages provided by embodiments of the present invention is theability to direct sintering or curing energy in a pattern thatcorresponds to the pattern of the printed ink. Wavelength selectivity isalso improved over conventional curing methods, enabling more efficientcuring and facilitating deposition and curing of multiple materials.Embodiments of the present invention may use one or more exposure levelsfor sintering nanoparticle materials.

These and other aspects, objects, features and advantages of the presentinvention will be more clearly understood and appreciated from a reviewof the following detailed description of the preferred embodiments andappended claims, and by reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a flow chart showing a sequence for printing and curingnano-materials for electronic applications, according to an embodimentof the present invention.

FIG. 1B is a schematic diagram showing a printing and curing system foruse with electronic ink.

FIG. 1C is a schematic diagram showing a printing and curing system foruse with electronic ink, wherein printing and illumination apparatusmove past a stationary substrate.

FIG. 2 is a schematic diagram that shows components of an illuminationapparatus for a printing and curing system using a bank of laser diodes.

FIG. 3 is a schematic diagram showing a printing and curing system usingtwo illumination apparatus for use with nanoparticle-based electronicink.

FIG. 4 is a schematic diagram showing a printing and curing system usingtwo printing apparatus and two illumination apparatus for use withelectronic ink.

FIG. 5 is a schematic diagram showing an illumination apparatus having amechanical dithering component.

FIG. 6 is a schematic diagram showing an illumination apparatus havingan optical dithering component prior to the illumination lens.

FIG. 7 is a schematic diagram showing an illumination apparatus havingan optical dithering component after the illumination lens.

FIG. 8 is a schematic diagram that shows a printing and curing systemusing a spatial light modulator.

FIG. 9 is a schematic diagram that shows spatial distribution of zeroth,first, and second orders of diffracted light from one type of spatiallight modulator.

FIG. 10 is a schematic diagram showing use of a phase modulation spatiallight modulator in an illumination apparatus according to an embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following is a detailed description of the preferred embodiments ofthe invention, reference being made to the drawings in which the samereference numerals identify the same elements of structure in each ofthe several figures. It is understood that the elements not shownspecifically or described may take various forms well know to thoseskilled in the art.

Where they are used, the terms “first”, “second”, and so on, do notnecessarily denote any ordinal or priority relation, but may be used formore clearly distinguishing one element or time interval from another.

In the context of the present disclosure, the term “ink” is a term ofart that broadly applies to a material that is deposited in a pattern ona substrate in a viscous, generally fluid form and is sintered andotherwise cured after deposition by applying a curing energy such asheat or light energy. Sintering is a curing process by which curingenergy effects a structural change in the composition of particles inthe ink. Curing may also have additional aspects for ink conditioning,such as sealing or removal of organic coatings or other materialsprovided in the ink formulation but not wanted in the final, printedproduct. In the context of the present invention, the term “curing” isused to include sintering as well as other curing processes that employthe applied light energy for conditioning the deposited ink.

The terms “nanoparticle-based material”, “nanoparticle-based ink”,“nanoparticle material” or “nanoparticulate material” refer to an ink orother applied viscous fluid that has an appreciable amount ofnanoparticulate content, such as more than about 5% by weight or volume.

In the context of the present invention, the term “substrate” refers toany of a range of materials upon which the nanoparticle ink is depositedfor curing. Exemplary substrates include plastics, textiles, paper,sheet materials, and other materials that provide a suitable surface fordepositing a pattern of nanoparticle-based ink.

As used herein, the term “energizable” relates to a device or set ofcomponents that perform an indicated function upon receiving power and,optionally, upon receiving an enabling signal.

The background section outlines a number of problems with conventionalmethods for sintering using Xenon light and other broadband lightenergy. Embodiments of the present invention address the problem ofcuring and sintering for nanoparticle-based materials using a lightsource that provides light to a spatial light modulator for forming apatterned illumination from the light. According to embodiments of thepresent invention, the spatial light modulator is energized and used sothat the patterned light energy extends across the width of a substrate,allowing single-pass curing of high volumes of material. Alternateembodiments enable curing in a swath that does not fully extend acrossthe width of the substrate.

There are a number of challenges that complicate the task of using laserdiodes for this purpose. One problem relates to the speed at which laserdiodes can be shuttled to deliver the necessary energy. Otherdifficulties relate to limitations of the laser devices themselves. Forexample, placing a bank of lasers in close proximity to a printingsurface can lead to optical feedback, jitter and other destabilizingeffects. Yet another challenge for a laser based system relates todelivery of uniform, dense, and addressable pixilation in illumination.

Laser thermal printing systems have been disclosed that use a fibercoupled diode array for dye sublimation and transfer. U.S. Pat. No.5,619,245, entitled “MULTI-BEAM OPTICAL SYSTEM USING LENSLET ARRAYS INLASER MULTI-BEAM PRINTERS AND RECORDERS” to Kessler et al., for example,describes a multi-beam laser printhead using a monolithic array ofindependently modulated diode lasers. Systems of this type deliver laserenergy with acceptable beam quality and energy characteristics fortransfer of a colorant from a donor to a recipient medium using ablationor other mechanisms. Optical characteristics such as depth of focus areoptimized for colorant transfer with these printheads. Registration andalignment of the printhead to the donor and recipient media are tightlycontrolled in this type of donor transfer printing apparatus, with tightconstraints on substrate spacing and handling. Energy levels that arelocally generated for donor ablation are quite high, suitable fordepositing a high-resolution array of colorant dots, but significantlyexceeding those needed for curing of applied nanoparticulate inks.

According to an aspect of the invention there is provided a method ofprinting high resolution electronic features by depositing a pattern ofnanoparticle-based ink onto a substrate and then curing the depositedpattern using fiber-coupled diode laser-based curing.

The flow diagram of FIG. 1A shows a sequence of steps for a printing andcuring method 10 for nanoparticle-based inks according to an embodimentof the present invention. This method includes: pretreating thesubstrate in a washing or cleaning step 20, depositing adhesionpromoting material in an optional coating step 30, depositing a patternof nanoparticle ink in a printing step 40; illuminating the pattern ofdeposited ink to transform the ink by sintering and other curingprocesses using a laser diode array in a curing step 50; and removingthe untransformed ink and residual materials in a removal step 60.Removal step 60 also includes evaporating and exhausting excess materialfrom the applied and cured ink or coating.

The schematic diagram of FIG. 1B shows a printing and curing system 80.The printing and curing system 80 has a substrate 120 on which materialis printed, a transport apparatus 90 with devices such as rollers 110 orother components for providing relative movement between printing andcuring components and substrate 120, a mount for substrate 120 which mayinclude a heat sink or temperature control element 100 designed tomaintain substrate 120 at a suitable temperature at specific points inthe process, an optional substrate cleaning apparatus 130, an optionalcoating apparatus 140, a printing apparatus 150 that is energizable fordeposition of the nanoparticulate electronic material, such as usinginkjet or screen print mechanisms, creating a pattern of printedelements 160 on the substrate 120 surface. An illumination apparatus 170has two or more energizable laser diodes 180, each with itscorresponding coupling optics 185 that direct light through acorresponding light guide, shown as an optical fiber 200. Light fromfibers 200 goes through a coupling block 210 and to an illumination lens220 for directing a pattern of illumination that corresponds to thepattern of printed elements 160 on substrate 120. A washing apparatus240 can be energized to perform a cleaning operation to remove uncuredink or other material. An exhaust element 250 is provided to help removeby-products of the printing and curing process.

Transport apparatus 90 more generally provides relative motion forforming a pattern and can also operate wherein substrate 120 isstationary and one or more of energizable surface conditioning,printing, and curing components, such as apparatus 130, 140, 150, 170,240, and 250 are swept along the surface of substrate 120 to performpattern deposition and curing operations. FIG. 1C is a schematic diagramshowing an alternate embodiment with a printing and curing system 88 foruse with electronic ink, wherein printing and illumination apparatus 150and 170 and other components are coupled together as part of a patternforming apparatus 94 that moves past a stationary substrate 120.Transport apparatus 90 may include a leadscrew or may be belt-driven,for example. A dashed box indicates pattern forming apparatus 94.Transport apparatus 90 moves pattern forming apparatus 94 from right toleft across substrate 120 in the arrangement of FIG. 1C.

Washing or cleaning step 20 in the sequence of FIG. 1A consists ofcleaning the substrate with solvents, or alternately with surfacetreatments such as using corona discharge energy or treating withcompressed gases or other methods. It is found that the method of thepresent invention is particularly suitable for, but not limited to, usewith a number of substrates including PET (polyethylene terephthalate),PI (Polyimide), PE (polyethylene), PP (Polypropylene), PVA (poly-vinylalcohol), SiN (silicon nitride), ITO (indium tin oxide) and glass. Ingeneral, substrates need to be sufficiently clean in order to fullyaccept and cure the printed ink materials. Failure to clean thesubstrate, either in line, by energizing substrate cleaning apparatus130 as depicted in the process of FIG. 1B, or prior to printing usingsome other method, can lead to poor adhesion, degraded electricalperformance, material contamination, and breakage.

According to an embodiment of the present invention, the substrate 120material is transported by means of transportation apparatus 90 (FIG.1B) and moved through system 80 in a roll-to-roll, flat, sheet-fed,drum-fed, continuous, or stop-and-start sequence. Along thetransportation system are placed one or more tracking elements such asreflectors or sensors 230. Tracking elements provide optical orelectrical feedback as to the alignment of the elements of the printingchain. For example, reflections of a tracking element in the curingprocess can determine curing accuracy and substrate position. Sensors230 can be placed under the substrate in the assembly or along edges ofthe substrate, as long as the illuminating wavelength reaches the sensor230.

Temperature control element 100 (FIG. 1B) may be a simple heat sink ormay be an apparatus designed to heat and cool the substrate to a desiredtemperature, integrated into transport apparatus 90. Maintainingtemperature becomes a concern, since heated substrates can expand orshrink under different temperature conditions, with the risk ofdeformation of substrate or end-printed structures. Furthermore, as heatenergy from the illumination system 170 can cause spatial temperaturevariations, spatially varying the temperature may be useful for certainapplications.

Optional coating step 30 in the FIG. 1A sequence prepares the surfacewith adhesion promoting materials. Coatings, applied by energizingcoating apparatus 140 in FIG. 1B, can be uniformly deposited, such as byaerosol application, roll coating, or other methods. Alternately,coatings are deposited selectively by inkjet deposition, or otherselective printing mechanism, such as aerosol jet. This step, while notrequired in all cases, can significantly enhance the ability of materialto adhere to substrate 120. Selective deposition of adhesion promotingmaterials can further assist in delineation between electrically activeprinted electronic structures and passive sections of a printed region.Auxiliary drying equipment, not shown in the FIG. 1B or 1C embodiments,may also be provided to facilitate drying or solidifying of an appliedcoating.

Continuing with the FIG. 1A sequence, the nanoparticle ink is depositedonto the substrate in printing step 40. The ink is deposited byenergizing nanoparticle ink printing apparatus 150. Nanoparticle inkprinting apparatus 150 uses a suitable deposition method such asink-jet, offset-lithography, screen printing, indirect or directgravure, flexography, aerosol application, or some other method. Thebinder and/or coating present in the nanoparticle ink helps to providean even distribution of the ink. The deposited layer can be of variablethickness and, in practice, is typically in the thickness range betweenabout 0.05-50 μm, but would not be limited to this range.

As shown in the perspective view of FIG. 2, drivers 300, under controlof a control logic processor 310, provide the energizing signals for theindividual laser diode 180 in each channel in illumination apparatus170. A small number of laser diodes 180 are shown in FIG. 2. Inembodiments of the present invention, numerous laser diodes 180 can beemployed. Laser diodes 180 are provided with an optional heat sink 320.Each laser diode has corresponding coupling optics 185. An optical fiber200 or other light guide then directs the generated laser light throughcoupling block 210 and lens 220. The laser diode 180 in each channel canbe independently energized or de-energized as needed. This allowsillumination apparatus 170 to direct light in a pattern, in conjunctionwith the operation and speed of transport apparatus 90. Advantageously,the pattern of illumination that is provided corresponds to the patternof nanoparticle material that is applied by nano ink printing apparatus150.

The use of laser light allows for the selection of a light wavelengththat is well suited for the sintering of the nanoparticles whileeliminating or minimizing damage to the coating. By using lasers,embodiments of the present invention apply monochromatic light to thesubstrate at wavelengths most favorable to sintering and other curingfunctions, without contributions from other wavelengths, such as lowerwavelength light that can be heavily absorbed in the upper layers ofdeposited material. As noted earlier, absorption of wavelengths in upperlayers nearest the surface can cause these upper layers to beinadvertently sealed, trapping binder and other materials that must beremoved from beneath the surface. Advantageously, laser illuminationprovides sufficient energy for the removal of component materials in theprecursor nanomaterial. This includes materials useful for improving inkapplication but not wanted in the final product, such as organic bindersand particle coatings. With laser light, the spectral content andintensity can be specified and controlled so that the laser delivers theproper energy to the applied material, at the proper depth. In this way,problems such as unwanted sealing of top layers can be avoided.

Thermal characteristics of the substrate can complicate the task ofsintering in a number of ways when conventional Xenon flash energy isused. Substrates having relatively high thermal conductivity, such asaluminum, silicon, and ceramic substrates, for example, can conduct theneeded heat away from the area of incident light before sintering energylevels are reached. Polymer-based substrates, such as ITO coated plasticsubstrates, can be damaged due to the higher thermal conductivity of theITO coating. Embodiments of the present invention help to addressproblems related to thermal response by using laser light that can befocused onto a small area.

Coupling of the laser light to each channel 212 within a coupling block210, as shown in FIG. 2, is managed carefully, since reflections fromthe fiber can cause inadvertent mode hopping and other instabilities.Techniques for laser light routing and coupling to prevent theseproblems are well known to those skilled in the optical design arts.Optical fibers 200 extend to the coupling block 210, which may consistof a series of V-grooves in which the fibers are nested. Typical fibersinclude 50 um step core index fibers with a Numerical Aperture (NA) of0.2. Choice of fibers takes into account that with lower NumericalApertures, the laser light will have a greater depth of focus.Subsequent illumination lens 220 transmits the generated light. The spotprofile of the directed laser beam can be round or slightly or highlyelliptical, depending on the cross array imaging of the printing lens.Laser diodes in the array have a first distance D1 between them,determined by factors such as size of components and thermalconsiderations. Coupling block 210 and optical fibers 200 enable laserdiode light channels to have a second distance D2 between them, whereinD2 is less than D1. Thus, features can be written at high resolution.Optical fibers are step-index optical fibers according to an embodimentof the present invention.

Commercially available solutions for driving the laser diode includeusing a 12 bit DAC that provides a high speed amplifier driving currentto each channel or a constant current source switching between the diodelaser and a dummy load to ensure a fast enough rise time, such as a <50ns rise time. The driver can use single pulses of light to deliverdesired peak intensity as well as to deliver total energy at a givenlevel. Amplitude modulation may be used. Additionally, due to the quickrise time, pulse width modulation, or some combination of modulationtechniques, can be used to the deliver the desired energy.

The resolution of the printing structure can be further determined bythe relative energy profile of the illumination beam at substrate 120and the response of the applied ink material. By way of reference, in adye sublimation printing system, a 50 um core fiber can produce a 2560dpi (dots-per-inch) image, with a spot size of 1 um. Similarly, in amaterial curing system, the printed electronic element can be smallerthan core beam size. This effect can be used to interlace wavelengthsand to obtain smaller features.

Using fiber coupled lasers allows a number of advantages, including ameasure of thermal isolation. The local temperature of the diode anddrivers can be separated from the printing environment. By mounting andspacing the laser diodes appropriately, feedback and jitter can beminimized. Using modular design techniques, laser assemblies can bereadily replaced. Embodiments of the present invention use one ofseveral ways to monitor diode operation. One technique is to maintain afeedback loop within driver 300 for adjusting drive current to withinprescribed values. Alternately, feedback from the illumination incidenton the substrate surface is used.

According to an embodiment of the present invention, diode laser arraysare formed of diodes having different emission wavelengths, wherein theemission wavelengths of at least two of the laser diodes in the arraydiffer from each other by more than 25 nm. By spacing optical fibers 200in the coupling block 210, the subsequent illumination lens 220accommodates accurate spot placement for each wavelength. There can besome trade-off of spot size verses proximity between the differentwavelengths. The focal spot size can also vary as a function ofwavelength.

Advantageously, separate channels can be addressed simultaneously orsequentially. With simultaneous addressing, printing relies on thedifference in required curing wavelengths for different materials. Forexample, ink having high copper (Cu) content tends to cure with appliedenergy in the near infrared, whereas some inks high in silicon requireshorter wavelengths.

When driving laser diodes, pulse width modulation (PWM) can be used forcontrolling power levels and for temporally interspersing theillumination wavelengths. This permits the use of different wavelengths,both to cure different materials and to provide curing energy atdifferent depths. For example, a longer wavelength can be useful forcuring material at a greater depth. Wavelengths that have been found tobe suitable for curing include, but are not limited to: 193 nm, 248 nm,308 nm, 355 nm, 488 nm, 532 nm, 808 nm, 860 nm, 975 nm, 1064 nm, and CO₂laser wavelengths.

Nanoparticle Ink Formulations

The printed electronic structures that can be formed by the presentmethod are made of a metal or semi-metal, such as semiconductormaterial. Suitable metals for printing and curing in a pattern include,but are not limited to, copper, gold, silver, nickel, and other metalsand alloys. Semi-metal materials including silicon can also be used.Furthermore, silicon particles that have been doped to providesemiconducting behavior (for example, doped with phosphorous or arsenic)are also suitable. Therefore, the present method can be used inproduction of both electronic structures, such as connecting tracesbetween devices, and semiconducting devices themselves.

The nanoparticle ink used in embodiments of the present inventioncomprises the metal or semi-metal with a binder or coating (typicallyorganic). The binder or coating in the ink helps to preventagglomeration and to maintain the surface area, which confers many ofthe advantageous properties of nanoparticles. The nanoparticles used inthe ink formulation can be between 0.5-500 nm. Advantageously,therefore, the present invention can be implemented for a wide range ofnanoparticle inks including those with larger particles which are oftencheaper to produce. An example of a suitable ink is the commerciallyavailable CI-002 formulation sold by Intrinsiq Materials, Rochester,N.Y. As noted previously, inks need not be comprised solely ofnanoparticles, but may contain a mix with at least some percentage ofnanoparticles, as described previously, and larger particles.

The high surface area of the nanoparticles is advantageous, so that theenergy required to transform the nanoparticles in the ink, such as bysintering or curing, is less than for bulk materials. Therefore, as thelaser illumination not only removes the coating or binding materials inthe ink formulation, it also causes a transformation of the material.Upon receiving the illumination energy, the individual metal/semi-metalnanoparticles bond to form a metal/semi-metal structure, in the form ofa densified metal or semi-metal film (depending on the material of thenanoparticle ink). As the laser illumination can be focused to a smallspot size, the metal structure that is formed is localized to areasimpacted by the laser. The high degree of accuracy with which the lasercan be directed results in the formation of the high resolution printedstructures.

Each deposited material or ink can have different curing properties,responding differently to light of various wavelengths and intensities.Where multiple materials are deposited, it may be suitable to cure thedifferent materials under the same conditions or to vary wavelength andintensity levels appropriately. According to an embodiment using asingle illumination apparatus 170 as in FIG. 1B, for example, each laserdiode 180 has the same wavelength, with variation in wavelength withinthe laser array to within no more than about +/−1 nm of a nominalwavelength, but the intensity of the directed illumination changes,depending on the spatial position of apparatus 170 relative to thesubstrate 120 surface. Individual laser diodes 180 can be energized atdifferent power levels over different portions of the applied pattern ofprinted elements 160. Exposure duration can also be modified, such as byvarying the transport speed of transport apparatus 90 or usingpulse-width modulation, for example. According to an alternateembodiment of the present invention, laser diode array 190 has laserdiodes 180 of different wavelengths, suitably positioned for providingenergy to the applied pattern of printed elements 160.

Referring again to the sequence of FIG. 1A, once the laser diode array190 has finished illuminating the substrate and the desired image hasbeen cured, the untransformed material is removed in removal step 60.The ink that has been scanned by the laser beam is transformed,typically by curing or sintering depending on the strength of the laserand length of exposure. The properties of the transformed, densifiedmetallic structure differ from the untransformed structure. It ispossible to select washing formulations and processes in removal step 60to remove untransformed, unbounded, or uncured materials from thesubstrate surface while having little or no impact on cured regions.Such washing formulations are well known in the art of photolithography.

It is found that the present method is particularly suitable for anumber of substrates including PET, PI, PE, PP, PVA, PI, SiN, ITO andglass. Therefore, the present application provides an improved methodfor producing high resolution lines compared to other systems. Inparticular, the direct transformation (curing, sintering or otherwise)of the material by the laser allows for higher resolution features,reduces or avoids the need for adding further layers such as photoresistlayers and requires fewer stages to produce than do conventionalmethods. Printing and curing of electronic materials and components canbe performed at low volumes as well as for large-scale, high volumeproduction.

The schematic diagrams of FIGS. 3 and 4 show alternate embodiments ofthe present invention for depositing more than a single material.Processing using these systems repeats portions of steps 40, 50, and 60in the FIG. 1A sequence.

In an alternate embodiment of a printing and curing system 82 as shownin FIG. 3, multiple separate illumination diode arrays 190 a and 190 bare used to provide extra spatial coverage and/or differentilluminators, such as diodes of different wavelength. An illuminationapparatus 170 a has a bank of multiple laser diodes 180 a that areenergizable to direct light through coupling optics 185 a to opticalfibers 200 a, coupling block 210 a, and an illumination lens 220 a.Similarly, an illumination apparatus 170 b has a bank of multiple laserdiodes 180 b that are energizable to direct light through couplingoptics 185 b to optical fibers 200 b, coupling block 210 b, and anillumination lens 220 b. Using separate illumination apparatus 170 a and170 b allows each of the subsequent illumination lenses 220 a and 220 bto be of simpler design, since the respective wavelength spread for eachlens can be minimized. The arrangement of printing and curing system 82is further beneficial where particular printed areas of substrate 120may need additional illumination or where there is component failure inone of illumination apparatus 170 a or 170 b.

Also shown in the embodiment of printing and curing system 82 in FIG. 3are multiple washing apparatus 240 and exhaust elements 250 for removingvolatilized material. Optionally, one set of washing and exhaustelements may suffice depending on factors such as materialcharacteristics and transport speed.

In an alternate embodiment, of a printing and curing system 84 as shownin FIG. 4, multiple printing apparatus 150 a, 150 b are used, along withcorresponding illumination diode arrays 190 a, 190 b. This arrangementallows additional spatial coverage for depositing the same material,including deposition at different feature sizes, or depositing andcuring different nanoparticle ink materials, such as materials withdifferent viscosities, requiring different preconditioning or curing, orhaving other different characteristics. Printing apparatus 150 a and 150b can be the same type or different types of print systems. For example,the first apparatus 150 a may be an inkjet printer, and the secondapparatus 150 b a gravure printer. In the particular embodiment shown inFIG. 4, two washing apparatus 240 and a single exhaust element 250 areshown; alternate embodiments with different numbers and arrangements ofthese support systems can also be provided, as described previously. Theuse of multiple illumination apparatus 170 a and 170 b provides the sameadvantages described with reference to FIG. 3. In addition, furthercoatings may be applied between printed layers of nanoparticlematerials, such as an insulating coating, for example.

According to an alternate embodiment of the present invention, theillumination that is used for curing is spatially dithered, or movedrapidly between nearby positions at a high rate of speed. Dithering canbe advantageous for increasing the area coverage of laser light beamswhere there are a limited number of light sources and for reducingexcessive patterning or other unwanted effects of the illuminationsystem. Embodiments of FIGS. 5, 6, and 7 show various mechanisms thatare energizable for dithering and that can be used for one or more ofillumination apparatus 170, 170 a, or 170 b in the embodiments shown inFIGS. 1B, 3, and 4. The schematic view of FIG. 5 shows one type ofmechanical dithering apparatus 600 that has an actuator 610 with acoupling 620 to optical coupling block 210. According to an embodimentof the present invention, actuator 610 is a piezoelectric actuator thatcauses dithering by rapidly vibrating coupling block 210. Alternately,actuator 610 can be coupled to other appropriate elements in the opticalsystem.

Spatial dithering can include the illumination lens 220 assembly or canbe within the field of view of the lens assembly. FIG. 6 depicts anoptical dithering apparatus 700. To provide dithering, a mirror element720 is coupled to an energizable actuator 710 to provide translation ineither or both linear and rotational directions, optically redirectingthe illumination in the optical path preceding the lens 220 assembly.This requires that the dithered light falls within the field of thelens. In an alternate embodiment shown in FIG. 7, the optical ditheringapparatus 700 is introduced in the optical path following illuminationlens 220. This design requires a sufficient depth of focus and focallength.

In cases involving dithering, alignment tracking is useful to helpprovide the illumination over the intended area. Sensors 230 and relatedcomponents (FIGS. 1B, 3, 4) help to provide the needed alignmenttracking.

Embodiments of the present invention can provide a measure of controlover how the curing illumination is directed to surface 120, both fordirecting a pattern of light and for dithering. The schematic diagram ofFIG. 8 shows an alternate embodiment of a printing and curing system 86of the present invention having an illumination apparatus 172 in which aspatial light modulator (SLM) 800 is used for directing laser light tothe substrate surface 120. Light from one or more laser diodes or otherlight source 820 is conditioned by a uniformizer 810 and directed to SLM800. Uniformizer 810 can be, for example, any suitable type of lighthomogenizer, such as a fly's-eye lens array, integrating rod, or otherlight integrator. Light sources used as part of light source 820 canemit light of the same wavelength or light of different wavelengths,that is, light of wavelengths that differ from each other by more than25 nm.

Spatial light modulator 800 pixelates the uniformized input beam,breaking it into independent, spatially identified, modulated portions.Each pixel is individually modulated temporally and with respect toamplitude. The individual pixels are re-imaged at the printing plane tosinter the deposited ink. With this arrangement, the laser light can bepulsed or continuous; the SLM 800 provides patterning and, optionally,dithering of the illumination light. Advantages of SLM systems include ameasure of control over light output, response speed, and uniformity.

Spatial light modulation can be liquid crystal devices (LCD) ormicromechanical-based modulation devices, such as digital micromirrorDMD array, such as the Digital Light Processor (DLP) from TexasInstruments, Inc., Dallas, Tex. With such devices, the light intensityat each pixel is controlled by the modulator output. Furthermore, withvery fast modulation, the total light intensity can be varied throughpulse width modulation and pulse frequency such that a cumulative energytarget is approached.

Spatial light modulators can also be electro-optic modulators wherebythe spatial intensity is modulated by means of electric field variationsin an electro optic material. An example of this type of device is theElectro-optic phase modulator from Xerox Corp., Stamford, Conn. Othertypes of phase modulation are provided by diffraction, using a GEMS(grating electromechanical system), such as that described in U.S. Pat.No. 6,411,425 to Kowarz et al. entitled “ELECTROMECHANICAL GRATINGDISPLAY SYSTEM WITH SPATIALLY SEPARATED LIGHT BEAMS”; a gratingmodulator array, such as that described in U.S. Pat. No. 6,084,626 toRamanujan et al. entitled “GRATING MODULATOR ARRAY”; or a GLV (gratinglight valve), such as that described in U.S. Pat. No. 5,481,579 entitled“FLAT DIFFRACTION GRATING LIGHT VALVE” to Bloom et al. Additionalmodulator types include semiconductor based SLMs.

The various types of SLM devices can directly modulate intensity(amplitude) or can operate using frequency/phase modulation. In the caseof phase modulated light modulation, light is selectively reflected ordiffracted into a number of light beams of discrete orders, forming afar-field pattern. This far-field pattern can then be filtered to allowpassage of select orders. Those diffracted orders are then reimaged tothe print surface, with modulation achieved by temporally deflectinglight into specified orders.

Example far field patterns are shown in FIG. 9. In systems that generatea far field pattern, a filter is used to select different orders oflight. Undeflected light, zeroth order light 824 is provided with theSLM in one state. Deflected light, shown in FIG. 9 as first order light828 and second order light 830, is provided with the SLM in an alternatestate. By selecting the zeroth order light 824, thresholdingapplications wherein a minimal light intensity is required can beenabled. By modulating light into its various orders, the pixel profileand width can be altered dynamically by means of addressing. Forexample, a spatial light modulator whose pixel is defined by the fieldprofile between electrodes, can effectively provide wider pixels bymaintaining a wider field profile. Also, field profiles can readily becontrolled to provide sub-pixelization and varied subpixel intensities.

The simplified schematic of FIG. 10 shows components of illuminationapparatus 172 using phase modulation. A laser or laser array 840provides light through uniformizing optics 844 to spatial lightmodulator 800. A far field 850 is formed between lenses 848 and 852,with a spatial filter 854 in far field position, generating imagedpixels at an image plane 860.

Embodiments of the present invention advantageously allow highresolution features to be produced in a single stage process. Inparticular, the invention avoids the need for an extra layer, such as aphotoresist layer, and its subsequent processing. Furthermore, unlikephotoresist methods, the method of the present invention does notrequire the use of etchants to remove the unprotected, uncuredstructure. This is advantageous as it simplifies the production process.In addition, embodiments of the present invention allow a measure ofaccuracy with direct placement of electronic traces and structures. Itis known, for example, that etchants used in conventional electronicpatterning can result in excessively sloped tracks or undercut, whereasthe use of lasers to directly cure/transform the material allows forwell-defined edges to be formed.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the scope of theinvention.

1. An apparatus for forming a pattern of a nanoparticle ink on asubstrate, the apparatus comprising: a transport apparatus that isenergizable to move the substrate in a direction; a printing apparatusthat deposits the nanoparticle ink in a pattern on a surface of themoving substrate; and an illumination apparatus that directs a patternedillumination to cure the deposited ink pattern on the moving substrate,the illumination apparatus having: (i) a light source that generateslight directed toward a uniformizer; (ii) a spatial light modulatorenergizable to form a patterned illumination from the uniformized light;(iii) an illumination lens disposed to direct illumination from thespatial light modulator onto the surface of the moving substrate.
 2. Theapparatus of claim 1 further comprising a spatial filter in a far fieldposition for selecting particular orders of diffracted light.
 3. Theapparatus of claim 1 wherein the spatial light modulator is a digitalmicromirror array.
 4. The apparatus of claim 1 wherein the spatial lightmodulator is a liquid crystal device.
 5. The apparatus of claim 1wherein the spatial light modulator is a phase modulator taken from thegroup consisting of a grating light valve, a grating modulator array,and a grating electromechanical system.
 6. The apparatus of claim 1wherein the light source comprises at least one laser.
 7. An apparatusfor forming a pattern of a nanoparticle-based ink on a substrate, theapparatus comprising: a printing apparatus that is energizable todeposit the nanoparticle-based ink in a pattern on a surface of thesubstrate; an illumination apparatus that directs a patternedillumination to cure the deposited ink pattern on the substrate, theillumination apparatus having: (i) a light source that generates lightdirected toward a uniformizer; (ii) a spatial light modulatorenergizable to form a patterned illumination from the uniformized light;(iii) an illumination lens disposed to direct illumination from thespatial light modulator onto the surface of the moving substrate; and atransport apparatus that is energizable to provide relative motionbetween the substrate and the illumination apparatus.
 8. The apparatusof claim 7 further comprising a spatial filter in a far field positionfor selecting particular orders of diffracted light.
 9. The apparatus ofclaim 7 wherein the spatial light modulator is a digital micromirrorarray.
 10. The apparatus of claim 7 wherein the spatial light modulatoris a liquid crystal device.
 11. The apparatus of claim 7 wherein thespatial light modulator is a phase modulator taken from the groupconsisting of a grating light valve, a grating modulator array, and agrating electromechanical system.
 12. The apparatus of claim 7 whereinthe light source comprises at least one laser.
 13. The apparatus ofclaim 7 wherein the transport apparatus moves the substrate past theillumination apparatus.
 14. The apparatus of claim 7 wherein the lightsource emits wavelengths that differ from each other by more than 25 nm.15. A method for forming a pattern of a nanoparticle ink on a substrate,the method comprising: energizing a transport apparatus to move thesubstrate in a direction; depositing the nanoparticle ink in a patternon a surface of the moving substrate; and curing the deposited inkpattern on the moving substrate by: (i) generating light and directingthe light toward a uniformizer; (ii) energizing a spatial lightmodulator to form a patterned illumination from the uniformized light;and (iii) directing the patterned illumination from the spatial lightmodulator onto the surface of the moving substrate.
 16. The method ofclaim 15 wherein energizing the spatial light modulator comprisesenergizing a phase modulator taken from the group consisting of agrating light valve, a grating modulator array, and a gratingelectromechanical system.
 17. The method of claim 15 further comprisingdithering the illumination from the spatial light modulator.